8 - types of dinosaurs

dinosauria

• Subset of dinosauromorpha

• Has some minor modification to some bones

  • Forearms are more powerful

  • Opening on each side of the hip where the femur is inserted

• Found muscle attachment scars on skulls showing that they had a very powerful bite

• Includes all birds and dinosaurs

  • All birds are dinosaurs but not all dinosaurs are birds

oldest fossils

• 28,000,000 years ago

  • Argentina

    • Had primitive traits

    • Bipedal

  • Brazil

• So previously thought that South America is where dinosaurs first appeared

  • Disproven: the rocks age was not common globally

• Oldest trackways

  • 242 to 237

• Dinosauromorphs

  • 244 to 242

norian time dinosaurs

• Dinosaurs on all of pangaea

• Diverse, widespread = evolution happened quickly after first appearance of dinosaurs

• Non dinosaur dinosauromorphs existed with dinosaurs but went extinct by the end of the late triassic

cause of diversity

• Diverse because reproductively isolated + ecological conditions caused them to be so different that they can't interbreed any longer

• Natural selection

  • Some traits were more beneficial than others

  • Depending on time and place

• ex. of eco conditions

  • Pangea broke up

  • Mountains eroded

  • New mountains formed

  • Rivers changed course

  • Sea levels changed and sometimes flooded the interior of continents

  • Temperature changes

  • Patterns of precipitation changes

defining species

• By seeing which animals are mating with each other

  • Cannot be found in the fossil record so this method is better for living organisms

• Exception

  • Asexual organisms

  • Some different species can meet with each other to form hybrids

morphospecies

• Some reliable characteristics that make them unique compared to all other species

• Used to define species in the fossil record

• Issue

  • The difference could be due to different reasons:

    • Individual variation, sexual dimorphism, ontogenetic change, incomplete fossil record

• So usually if two specimens look different then they are probably identified as two different species

gender in fossil record

• Genitals do not get preserved

• Look for eggs in the body cavity or Medullary bone

  • The absence of them does not automatically make it a male though

• Size difference

  • Males are not always bigger than females

• Ornamentation

age in fossil record

• LAGs

  • Lines of arrested growth

  • Found in bones and teeth

  • Form seasonally

  • Counted to estimate the age

• Lack of fusion and skull bones = juvenile

• Spongier bones = young

• Solid bones = adult

ex. nanotyrannus

• Not sure if it's a young T Rex or a dwarf of another species or a juvenile of another species

• Small, spongy bone = juvenile

• Fused skull = adult but still could be juvenile

• Lower jaw has 17 teeth on each side while the T Rex has 11 to 14 on each side

  • T Rex could lose teeth as they age or there could be natural variation

• Differences in the skull and skeleton in terms of proportion and shape and the presence of a dental groove

  • Due to ontogenetic variation or are they part of another group?

major dinosaur groups

1. theropods

   • Mostly carnivorous

   • ex. T Rex

2. Sauropodomorphous

   • Long neck dinosaurs

   • ex. Brachiosaurus

3. Ornithischians

   • All the other dinosaurs

• No debate

historical subdivisions of dinosauria

• Since 1887 The three groups were divided into two clades

  • Saurischia

    • Therapods, sauropodomorphs

  • Ornithischia

• Harry Sealy said that all dinosaurs have 3 bones that make up the pelvic girdle

  • Ilium

  • Ischium

  • Pubis

• pubis is oriented into two ways

  • Down (Towards the head) and forward = saurischians

    • Lizard hipped

    • But birds are actually saurischian dinosaurs evolved from theropods

  • Part of the pubis points backward = ornitischians

    • Bird hipped

    • Lies along the lower rim of the ischium

    • This lineage is extinct

ornithischia

• They all have many common characteristics

  • So more well defined

saurischia

• Only have a few common characteristics

  • So probably were prey

  • Less well defined

• Not totally carnivorous but probably primitively

• Long vertebrae in the neck

• Large hands

• No fifth finger

• thumb can crossover the palm

feathers

• Mostly found in therapods

• 2009 - tianyulong

  • Ornithischian dinosaur

  • Simple feathers on beak, back, tail

• So then feathers had to have evolved twice or as a primitive feature of all dinosaurs

• 2019

  • Pterosaurs were found to have had primitive feather like structures

• So feathers may have been a diagnostic characteristic of all ornithodirans

reorg. of groups in dinosauria

• 2017 Baron

• Proposed an new cladogram that group therapods and ornithischians into a new group called ornithoscelida Based on the principle of parsimony

• Suggests that hips are not a diagnostic character

• 2 main branches are now

  • Sauropoda

  • ornithoscelida

    • Theropoda

    • ornithischia

• Evidence

  • Some members of ornithischians, theropoda have feathers or feather like structures but sauropodomorphs and Herrerasaurids seem to not

  • Primitive ornithischians looked similar to therapods

  • Doesn't make sense for birds to be lizard hipped dinosaurs

• Issues

  • sauropodomorphs and therapods have pneumatic bones AKA bones with air sacs but ornithischians do not

    • But pterosaurs do so it could just be a primitive trait of all ornithodira

  • Requires carnivory to evolve twice

    • Once in therapods and then again in Herrarasaurids

• So still not sure